1. Field of the Invention
The present invention relates to a photomultiplier having a photoelectric surface for photoelectrically converting incident light and emitting electrons, and a plurality of stages of dynodes for multiplying the electrons.
2. Related Background Art
A photomultiplier has a photoelectric surface(photocathode) for converting incident light into electrons, dynodes for multiplying the electrons, and an anode for collecting the electrons, and is used to detect weak light. A conventional photomultiplier using box-and-grid dynodes and mesh-type dynodes is known in Japanese Patent Laid-Open No. 59-108254.
As a conventional photomultiplier using in-line dynodes is known. The in-line dynode is used as a head-on type photomultiplier. In such an in-line dynode, however, the distance between the photoelectric surface and the anode is long, resulting in a bulky photomultiplier. To solve this problem, a device constituted by combining a box-and-grid type photomultiplier and a mesh type photomultiplier is described in Japanese Patent Laid-Open No. 59-108254.
The photomultiplier with a flat structure is excellent because of its low dependency of time characteristics on an incident position and high operability in a high magnetic field. However, the response speed is lower than that of an in-line photomultiplier. Additionally, when the above mesh type dynode is used, electrons pass through the mesh (.eta.=40%), and a gain per unit dynode becomes low. To obtain a sufficient gain, ten stages of dynodes are required.